THE city’s plan to charge motorists $8 to enter Manhattan has put it on a collision course with the State Department, which has started a trans-Atlantic war by refusing to pay a similar fee imposed in London.

Aides to Mayor Bloomberg insist everyone, with the exception of the handicapped, taxi and livery drivers and those in emergency vehicles, would be included if his congestion-pricing plan is approved by Albany.

There’s no mention of diplomats or, for that matter, government employees.

“We see it as a user fee,” said mayoral spokesman Stu Loeser. “It’s much as if someone wanted to park a car with diplomatic plates in a municipal lot. They’d have to pay.”

That’s not the way the State Department sees it.

In a directive issued last May, it described London’s congestion pricing fee as a “tax.”

In this case, the terminology couldn’t be more important.

Governments are exempt from taxes under the Geneva Convention.

So, in 2005, the U.S. Embassy in London simply stopped paying when its diplomats wheeled into the congestion zones.

The congestion charge in London is $16 a day at current rates of exchange.

Matt Brown, a spokesman for London Mayor Ken Livingstone, said the United States now owes about $3 million, which includes hefty fines.

Janelle Hironimus, a State Department spokeswoman, noted that several other governments are in the same boat.

“Many other countries are not paying the tax, so we are not alone in our legal position,” Hironimus said.

She explained that diplomats pay only charges tied to specific services, such as tolls that go toward bridge and road maintenance.

It’s not clear how the British government will respond when its diplomats here are hit with a congestion charge similar to the one U.S. officials refuse to pay in London.

Turnabout would certainly be fair play.

But the situation is complicated by the fact that British Prime Minister Tony Blair made a surprise video appearance at Bloomberg’s speech on the environment last Sunday and praised his leadership.

A spokeswoman for the British Consulate said it wouldn’t make any decision before Bloomberg’s plan actually wins approval.

Walter McCaffrey, chief spokesman for the anti-congestion pricing lobby, predicted that foreign governments would follow the example set by the State Department. “They’ll just ignore it,” he said.

McCaffrey conceded one point he didn’t have to: “We consider it de facto a tax. But legally, it’s not a tax. The distinction is lost on motorists.”